The invention relates to a motor in which a current path is electronically altered by means of plural transistors.
Recently, motors in which a current path is electronically altered by means of plural transistors have been widely used as driving motors for an OA apparatus or an AV apparatus. In a prior art example of such a motor, a current path to windings is electronically altered by using PNP-type and NPN-type power transistors.
FIG. 25 shows a motor of the prior art. The operation of the motor will be briefly described. A rotor 2011 has a field part configured by permanent magnets. A position detecting block 2041 produces two sets of three-phase voltage signals K1, K2, and K3, and K4, K5, and K6, responding with the rotation of the rotor 2011. A first distributing block 2042 produces three-phase lower-side conduction control signals L1, L2, and L3 responding with the voltage signals K1, K2, and K3, to control the conduction of lower-side NPN-type bipolar power transistors 2021, 2022, and 2023. A second distributing block 2043 produces three-phase upper-side conduction control signals M1, M2, and M3 responding with the voltage signals K4, K5, and K6, to control the conduction of upper-side PNP-type power transistors 2025, 2026, and 2027. According to this configuration, three-phase drive voltages are supplied to windings 2012, 2013, and 2014.
However, this prior art motor has the following problems.
(1) Large Power Loss
In the configuration of the prior art, the emitter-collector voltages of the NPN-type power transistors 2021, 2022, and 2023, and the PNP-type power transistors 2025, 2026, and 2027 are analoguely controlled so as to supply drive currents of an amplitude required for the windings 2012, 2013, and 2014. In each of the power transistors, therefore, the voltage drop across the power transistor is large, and a large power loss is generated by a product of the voltage and the current of the power transistor. Particularly, the drive currents of the motor windings are large and the power loss is extremely large. As a result, the motor has a very low power efficiency.
(2) High Production Cost
In order to reduce the production cost, it is effective to assemble transistors, resistors, and other devices into a one-chip integrated circuit (IC). However, the formation of the PNP-type power transistors 2025, 2026, and 2027 requires a large chip area, thereby producing a large factor of increasing the production cost. Because of an effect due to a parasitic capacitance formed as a result of the integration, the PNP-type power transistors are difficult to operate at a high speed. Since the power transistors consume a large power and generate a large amount of heat, moreover, it is difficult to integrate power transistors into one chip. Particularly, the drive currents of the motor windings are large and hence there is a high risk that heat generated by the power transistors causes a thermal breakdown of an integrated circuit to occur. When a heat radiating plate is attached to an integrated circuit in order to prevent a thermal breakdown from occurring, the production cost is greatly increased.
(3) Large Motor Vibration
In recent optical disk apparatuses such as a DVD-ROM or magnetic disk apparatuses such as an HDD, a motor with small vibration has been requested as development of recording and/or playbacking of a high-density disk. In the configuration of the prior art, however, rapid switching of a power transistor causes a spike voltage to be produced in a winding, thereby pulsating the drive current. As a result, the generated force of the motor is pulsated and a large motor vibration occurs.
It has been eagerly desired to develop a motor in which each of or all of these problems are solved.
The object of the present invention is to dissolve the above-mentioned various problems one by one or at the same time, and to provide a motor which is suitable for combination with an integral circuit.